This invention relates to the field of power conversion, and more particularly to the fields of controlling the current drawn from an AC input by rectification circuitry, power factor correction and reducing harmonic currents.
When the voltage from an AC power source is rectified to produce a DC voltage, as is commonly done in AC-line-powered electronic equipment, the harmonic content of the current drawn from the AC power source, and the power factor that the equipment presents to the AC line, will depend on the rectification method used. Capacitively loaded rectifiers, such as bridge rectifier 10 connected to filter capacitors 16 and 18 as shown in FIG. 1, conduct a large peak current during a small fraction of each AC power line cycle during which energy is delivered to the DC storage capacitors 16, 18. The current drawn by such a rectifier and filter capacitor circuit is rich in harmonics that contribute to power losses in the power distribution wiring without contributing to delivery of real power to the load.
Equipment designed to operate on worldwide AC power lines will typically need to operate over a total range of operating line voltages between 90 VAC and 270 VAC, rms, the lower segment of the range (90 to 135 VAC, rms) being typical of US and Japanese AC utility lines and the higher segment of the range (180 to 270 VAC) being typical of European lines. To accommodate both voltage ranges, the rectifier-capacitor circuit may include a range selection circuit to maintain the average value of the load voltage, VDC, within a range of approximately 250 to 380 VDC. Referring to FIG. 1, the range selection circuit may include a switch 12 which when open configures the rectifier as a bridge rectifier loaded by the series combination of capacitors 16 and 18. When closed, the switch 12 configures the rectifier as a half wave rectifier individually charging capacitor 16 during the positive half cycles and capacitor 18 during the negative half cycles. The rectifier-capacitor circuit thus functions as a voltage doubler when the switch 12 is closed. The switch 12 may be controlled either manually or automatically.
One way to control the harmonic content of the current drawn from an AC power source is to use high frequency switching xe2x80x9cpower factor correctionxe2x80x9d (xe2x80x9cPFCxe2x80x9d) circuitry or converters to control the waveform of the AC current to closely conform to the waveform of the AC source voltage. High frequency switching PFC circuitry is discussed in U.S. Pat. No. 5,321,348, entitled xe2x80x9cBoost Switching Power Conversionxe2x80x9d by Vinciarelli et al. and U.S. Pat. No. 4,677,366 entitled xe2x80x9cUnity Power Factor Supplyxe2x80x9d by Wilkinson. Referring to FIG. 2, another PFC approach uses an inductor 14 between the AC power source and the rectifier to reduce the harmonic content of the current drawn from the AC source. In another variation, described in U.S. Pat. No. 4,831,508, entitled xe2x80x9cPower Supply System Having Improved Input Power Factor,xe2x80x9d by Hunter, a voltage range switch is used to configure two inductors on the input side of the bridge rectifier either in series or in parallel and a line frequency operated shunt switch is used to enhance the effectiveness of the PFC circuit of FIG. 2. Each approach presents trade-offs such as higher cost and reduced efficiency of high frequency switching PFC converters, increased size and weight with passive approaches, and the higher cost and size and weight penalties of the low frequency switched PFC circuits.
The invention passively controls the current drawn from an AC input and delivers a DC voltage to a load.
Thus, in general, in one aspect the invention features a rectifier having inputs for receiving power from the AC input and outputs for delivering a rectified output. An output filter capacitance is connected across the load and an inductance is connected between the rectifier and the capacitor. A switch is connected to effect voltage doubling in a second position.
In general, in another aspect, the invention features a rectifier having inputs for receiving power from the AC input and outputs for delivering a rectified output and an output filter capacitance is connected across the load. First and second inductances are connected to carry current from the rectifier output to the capacitance. A switch is connected to allow current to flow in the first and second inductances during both half cycles of the AC input with the switch in a first position and to prevent current from flowing in the first inductor during negative half cycles and in the second inductor during positive half cycles with the switch in a second position.
In general, in another aspect, the invention features a bridge rectifier having a first and a second input for receiving power from the AC input, a positive output, and a negative output and two capacitances each having one plate connected to a center tap and one plate connected to a respective end tap. A first inductance is connected in series between the positive output of the bridge rectifier and a first end tap and a second inductance is connected in series between the negative output of the bridge rectifier and second end tap. A range switch is connected in series between the second input of the bridge rectifier and the center tap for doubling the output voltage when the switch is closed. The first and second end taps are connected to feed the load.
Implementations of the general invention may include one or more of the following features. The inductances may be magnetically coupled to provide mutual inductance. The inductances may be poled such that the flux generated by a current flowing from the positive output of the bridge rectifier to the first end tap aid the flux generated by a current flowing from the second end tap to the negative output of the bridge rectifier. The inductances may be the same. The first inductance may carry current during the positive half cycles of the AC input and the second inductance may carry current during the negative half cycles of the AC input. The first and second inductances may carry current during every half cycle of the AC input. The switch may be a single-pole switch. The capacitance may be a three-plate integrated capacitor. The inductance may be enclosed in a thermally conductive encapsulant-filled enclosure. The enclosure may include a thermally conductive base plate. The rectifier may be encapsulated with the inductances in the enclosure. Control circuitry for the switch may be encapsulated with the inductances in the enclosure. The capacitances may be physically external to the inductance enclosure. Switch control circuitry for sensing the AC input voltage level may operate the switch to effect voltage doubling when the level is below a predetermined threshold. The rectifier, switch, and switch control circuitry may be packaged in a first module. The inductances may be packaged in a second module. The modules may include a base plate and be filled with a thermally conductive encapsulant for removing heat. The capacitances may be physically external to the first and second modules. The inductances may have an inductance value that causes attenuation of odd current harmonics by at least 8 percent compared to an equivalent apparatus with zero inductance. The inductances have an inductance value that causes attenuation of current harmonics in an amount sufficient satisfy the requirements of EN61000-3-2 compared to an equivalent apparatus with zero inductance.
In general, in another aspect, the invention features a rectifier having first and second inputs for receiving power from the AC input and outputs for delivering a rectified output. A first inductance is connected between the first input and the AC input and a second inductance is connected between the second input and the AC input. An output filter capacitance is connected across the load and a switch is connected to effect voltage doubling in a second position.
Implementations of the general invention may include one or more of the following features. The rectifier may be a bridge rectifier. The switch may bypass the second inductor in the second position. The rectifier may be connected as a full wave rectifier when the switch is a first position. The current may flow in the first and second inductances when the switch is in the first position and only in the first inductor when the switch is in the second position. The filter capacitance may include a first capacitance and a second capacitance connected in series at a center tap. The apparatus switch, when in the second position, may provide a closed circuit between the center tap and one side of the AC input. The filter capacitance may be a three-plate integrated capacitor. The inductance of the first inductor may equal the inductance of the second inductor and the resistance of the first inductor may be less than the resistance of the second inductor. The resistance of the first inductor may be half of the resistance of the second inductor. The inductors may be magnetically coupled to provide a mutual inductance. The inductors may be poled such that the flux generated by a current flowing in the first inductor from the AC input to the rectifier aids the flux generated by a current flowing in the second inductor from the rectifier to the AC input. Switch control circuitry for sensing the AC input voltage level may operate the switch to effect voltage doubling when the level is below a predetermined threshold. The rectifier, switch, and switch control circuitry may be packaged in a first module. The inductances may be packaged in a second module. The modules may include a base plate and be filled with a thermally conductive encapsulant for removing heat. The capacitances may be physically external to the first and second modules. The inductances may have an inductance value that causes attenuation of odd current harmonics by at least 8 percent compared to an equivalent apparatus with zero inductance. The inductances have an inductance value that causes attenuation of current harmonics in an amount sufficient satisfy the requirements of EN61000-3-2 compared to an equivalent apparatus with zero inductance.
In general, in another aspect, the invention features a rectifier having first and second inputs for receiving power from the AC input and outputs for delivering a rectified output. A series circuit, including a first inductance and a second inductance connected at a center tap is connected between the AC input and the second input. An output filter capacitance is connected across the load and a switch is connected to the center tap to effect voltage doubling in a second position.
In another aspect the invention features a three-plate integrated capacitor.
In another general aspect, the invention features two inductors enclosed in an encapsulant filled enclosure. The enclosure may include a thermally conductive base plate. A rectifier may be encapsulated with the inductances in the enclosure. Control circuitry may be encapsulated with the inductances in the enclosure. The capacitances may be physically external to the inductance enclosure. The encapsulated module may provide passive harmonic current reduction to meet applicable international requirements with high power density (i.e., 200 Watt/cubic inch) and high efficiency (i.e., greater than 95%).
In general, in another aspect, the invention features a thermal management enclosure housing internal circuitry. The housing includes a thermally conductive base plate, an electrically insulative cover, input terminals for connection to an AC input, output terminals for connection to a load, and a thermally conductive encapsulant for filling the free space within the enclosure. The internal circuitry includes a rectifier having inputs connected to the input terminals for receiving power from the AC input and outputs for delivering a rectified output. An inductance is connected between the outputs of the rectifier and the output terminals and a switch is connected to effect voltage doubling in a second position.
Implementations of the invention may include one or more of the following features. The internal circuitry may include a switch controller connected to control the switch. The internal circuitry may require a filter capacitor to be connected to the output terminals for the voltage doubling.
In general, in another aspect, the invention features a thermal management module including at least two input terminals for connection to the AC input, a positive output terminal and a negative output terminal for connection to a load, a third output terminal for connection to a filter capacitance, and a thermally conductive encapsulant for filling the free space within the module. Passive internal circuitry includes rectifiers for receiving an AC input and delivering a rectified output, range selector circuitry connected to the third output terminal to effect voltage doubling, and range control circuitry for sensing the AC input level and controlling the range selector circuitry to activate the voltage doubling function when the AC input is below a threshold. The module requires a filter capacitance to be connected to the third output terminal for voltage doubling.
Implementations of the invention may include one or more of the following features. The module may further require an external inductance to control the current drawn from the AC input. The internal circuitry may include an inductance to control the current drawn from the AC input. The inductances may have an inductance value that causes attenuation of odd current harmonics by at least 8 percent compared to an equivalent apparatus with zero inductance. The inductances have an inductance value that causes attenuation of current harmonics in an amount sufficient satisfy the requirements of EN61000-3-2 compared to an equivalent apparatus with zero inductance. The internal circuitry may require two filter capacitors, one connected between the positive and third outputs and the other connected between the negative and third outputs.
The module may perform passive power factor correction. The module may perform passive harmonic current control.
In general, in another aspect, the invention features at least two inputs for receiving power from an AC source and at least two outputs for delivering the rectified voltage to the load.
Unidirectional conduction paths between the input and output rectify the AC input. At least one filter capacitance is connected across the output. First and second inductances are connected to carry current between the input and the load and have an inductance value, L, which causes attenuation of odd harmonic currents drawn from the input by at least eight percent compared to an equivalent apparatus having zero inductance. A switch is connected to in a second position to effect voltage doubling and prevent current from flowing in one of the inductances.
Implementations of the invention may include one or more of the following features.
The switch may prevent current from flowing in the second inductance during positive and negative half cycles of the AC input. The switch may prevent current from flowing in the first inductance during positive half cycles and in the second inductance during negative half cycles of the AC input.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.